Over 10% Efficient Pure CZTSe Solar Cell Fabricated by Electrodeposition with Ge Doping

The fabrication of kesterite CZTSe solar cells via an electrodeposition method provides an attractive approach for the low‐cost and environment‐friendly energy supply, yet the highest conversion efficiency for such solar cells (around 9%) is still far away from the highest efficiency of Cu‐based kesterite solar cells. Herein, a 10.54% efficient CZTSe solar cell (0.28 cm2 active sized area, without an antireflection layer) is developed by introducing electrodeposited Cu–Ge alloy layer at the bottom of metal precursor. It is found that the presence of Ge element within the bottom of the film can promote downward diffusion of Sn element. Consequently, the distribution of Sn is relatively homogeneous during the annealing process; thus, the formation of undesirable defect clusters is inhibited and the band alignment of the CdS/CZTSe interface is optimized. As a result, the conversion efficiency of CZTSe thin‐film solar cells is increased from 6.74% to 10.54%, which is the highest efficiency reported for electrochemically fabricated CZTSe solar cells. Cu–Ge alloy is electrodeposited at the bottom of Cu/Sn/Zn metal stacks. The presence of Ge leads to Sn downward distribution behavior, thus resulting in the inhibition of defect clusters and favorable band alignment. Finally, a champion solar cell with 10.54% efficiency is fabricated, which is the highest efficiency for electrodeposited Cu2SnZnSe4 solar cells.